Manufacture of monoalkali-metal phosphate.



UNITED STATES PATENT ornion. I

EMERSON HLSTBICKLER, OF NEW YORK, N. Y., ASSIGNOR TO GENERAL CHEMICAL COMPANY, OF NEW YORK, N. Y., A CQRPORATION OF NEW Y ORK.

MANUFAtlTUBE OF MONOALKALI-METAL PHOSPHATE.

No Drawing.

To all whom it may concern Be it known that I, EMnRsoN H. STRIGK- mm, a citizen of the United States, and a resident of the city ofNew York, State of New York, have invented certain new and useful Improvements in the Manufacture of Monoalkali-Metal Phosphate, of which the following is a specification.

My invention relates to of mono-alkali metal phos hates, an example of which is mono-so 'um phosphate, which is stated to have, apart from water of crystallization, the formula NaI-I PQ An object of my invention is to provide a novel process for the production of monoalkali metal phosphates by WhlCll a substantiallyv pure product is capable of being obtained on a commercial scale and at a commercially reasonable cost.

Another object is to provide a cyclic process forthe productionof mono-alkah metal phophate in which the residue, after the mono-alkali metal phosphate has been separated out, is introduced into an earlier stage of the complete rocess, such as that sta e at which tri-alka i metal phosphate is ma e for example in accordance with the process set forth in my Letters Patent No. 744,128, dated November 17, 1903, or in my Letters Patent No. 1,037,837, dated September 3, 1912.

tion of my invention, in which, as well as in the appended claims, I use the term alkali metal phosphate to include the di-and tri-alkali-metallic salts of phosphoric acid, such as sodium or potassium; tri-alkali metal phos hate to include trisodium phos hate an tri-potassium phosphate di-al ali metal phosphate to include di-sodium phosphate and di-potassium phosphate; mono-alkali metal phosphate to include mono-sodium phosphate and mono-potassium phosphate; and acid to include acids free from phosphorus such as sulfuric, nitric, hydrochloric and acetic acids. Heretofore mono-sodium phosphate has been a laboratory product only. The laboratory methods of producing it are (1) treating phosphoric acid (H,PO,) with sodium carbonate until the mixture is neutral, using methyl orange as an indicator; (2) treating tri-sodium phosphate or di- Speciflcation of Letters Patent.

the manufacture Other objects will be pointed out or .1111.

Patented Aug. 24., 1915.

Application filed March 22, 1912. Serial No. 685,584.

sodium phosphate with phosphoric acid; or

(3) adding alcohol to a solution of di-sodium.

phosphate in nitric acid.

For commercial and technical purposes, none of the above methods are-of utility in obtaining a pure mono-sodium phosphate, principally owing to the presence of impurities, such as iron, alumina, fluorin and organic matter, always contained in commercial grades of phosphoric acid, which impurities are not removable therefrom by commercial and technical operations and which contaminate the mono-sodium phosphate produced therefrom in accordance with the first two of the above laborator methods and, in the case of the third laboratory method, owing to the prohibitive cost of the alcohol. On the other hand my improved process of making mono-alkalimetal phosphates, which, of course, includes mono-sodium phosphate,.is both a commercially available process and one which re: sults in a product commercially free from iron, alumina, and the other impurities above mentioned, a product which is only accompanied by small and, for practical purposes, negligible amounts of other alkali-' metal salts, such as, for example, sodium sulfate, sodium chlorid, sodium nitrate or sodium acetate. By proper methods of purification, such as crystallization, the amounts of such accompanying salts can be reduced to any desired degree.

Broadly stated one form of my invention consists in dispensing with the use of phosphoric acid, and in treating an alkali-metal phosphate with an acid free from phosphorus, such as sulfuric acid, hydrochloric acid, nitric acid, which are mineral acids, or acetic acid, which is an organic acid, in such a manner as to produce mono-alkali metal phosphate, and separating this product from the salt of the acid which has been used, without the assistance of alcohol.

Any of the above acids may be added to tri-sodium phosphate, for example, in such amount that mono-sodium phosphate is produced together with the corresponding sodium salt of the added acid.

My invention contemplates a number of modifications in the manner of separating the mono-alkali metal phosphate and the salt of the added acid produced by the above process. The salt of the added acid, in some cases, may be separated out in solid form from the hot liquor, the mono-alkali metal phosphate being contained in the liquor resulting after such separation has been effected, and being separated from said resulting liquor in such manner as will hereinafter be set forth. In other cases the mono-alkali metal fphosphate may be separated out in solid 7 I have found that if tri-sod ium phosphate or di-sodium phos hate or diotassium phosphate be treate with a su cient amount of sulfuric acid, or hydrochloric acid, or nitric acid or acetic acid to produce I so '. Letters Patent No.-

x In the mono-alkali metal phosphate, substantially all of the latter may be separated from the according to my invention, utilized in the roduction of tri alkali metal phosphate as or example, by the process described in my 44,128, or my Letters Patent No. 1,037,837 hereinbefore mentioned, which tri alkali metal phosphate may be used in the present process of making mono-alkali metal phosphate. There is thus evolved a cyclicprocess in which all ofthe alkali metal products of phosphoricacid are utilized. The mono-alkali. metal phosphate moreover is produced in a substantially pure condition. When the cyclic rocess is used a complete separation o the mono-alkali metal phosphate and the salt of the added acid'is obviously unnecessary because in any case all of the phosphorus condtained the original phosphate is utilize practice of that example of my cyclic process in which I em loy sulfuric acid as the added acid, and w ich includes the process set forth in the above patent,

tri-sodium. phosphate is made, by treating rock-phosphate e. calcium phosphate with a solution'of niter cake and furnacing the solution thus obtained int-he presence of a carbonaceous material, the trl-sodium phosphate thus made is then treated with sulfuric acid in such a manner as to r0- duce mono-sodium phosphate and so 'um sulfate, the last mentioned salts are then separated, and the sodium sulfate, 'carrying with it small amounts of phosphate, is then utilized, as above set forth, in the manufacture of more tri-sodium phosphate. I have described my cyclic process in which sul furic acidvis used'and' the sulfate of soda produced is employed in the preparation of tri-sodium phosphatel It will be understood, however, that the salts of the other added, acids may by suitable modification orm,-whether the liquor be hot or cold.

be employed with equally successful results. If another acid than sulfuric has been used, the salt of the added acid may obviously be converted into a sulfate by treatment with sulfuric acid so that the processes hereinbefore referred to may be utilized for producing tri-alkali metal phosphate. To the sodium sulfate, produced or recovered in whatever way, the proper amount of crude phosphoric acid should be added so that the proportion between the sulfur and the phosphorus in the resulting mix is that presented in the above referred to patent.

I-have further discovered that the separation of the mono-alkali metal phosphate and the salt of the added acid is dependent in large measure upon the particular alkali metal in the phosphate and the particular acid which has been added. In the process of makin mono-sodium phosphate in which sulfuric, ydrochloric "or nitric acid is used,

the. resulting sodium sulfate, chlorid'or nitrate is first separated out from the hot solution, suitably concentrated; but, when acetic acid is used, the mono-sodiiun phos-' phate is preferably first separated out. In separating by crystallizatlonby cooling when sulfuric or. nitric acid is used, the

. phosphate is first separated out.

In making mono-potassium phosphate,

potassium sulfate is preferably separated 1 out first, whereas potassium chlorid, m-

trate or acetate is separated out last. In separating by crystallization, when acetic acid is used, the phosphate is separated out first; when hydrochloric acid is-used, separation by cold crystallization is not so efficacious as hot separation. A

'lhenature of my invention isclearly disclosed by the following. specific examples showing various 'methods of producing mono-alkali metal phosphate from alkali metal phosphate, all of which methods are Within the confines of'my invention. In

these examples, where parts are given they are to be understood as parts by weight.

In theniI have described my cyclic process only in connection with my preferred acid, which is sulfuric acid.

OPERATING WITH DI-BODIUM PHOSPHATE... Crystallized" di-sodium phosphate contains approximately 12 molecular proportions of water of crystallization; i. e. ap-' proximately 60% of water. In carrying out my .new' process with this product I have found it advantageous to take into account the solvent action of the introduced into the process and in the case of an acid "stead of di-sodium phosphate in all of the processes described for the latter, the processes and results being substantially the same.

A. Using sulfuric acid as the added acid.

Ewcmple I.

be, by boiling or evaporation until the solution filtered free of the undissolved material tests 60 B. at boiling temperature.-

Remove the material which separates out in solid form (largely if not wholly sodium sulfate) by filtering or other suitable knownv method, keeping the solution hot during this removal. Dilute the filtrate with water to approximately B. and allow it to. cool and crystallize. .dium phosphate. Concentrate the mother liquor by boiling to 50 B., allow it to cool and crystallize. This yields a second crop of mono-sodium phosphate. Continue concentration of the mother liquor and crystallization until the product runs too high in sulfate. At this stage it is returned, together with the sodium sulfate, separated during the evaporation, to the sodium phosphate process described in Patent N 0. 744,128. Instead of boiling down until the solution, free of undissolved material, tests 60 B. as just described, and separating it all at one time, it may be separated by filtering or otherwise, at two or more different timesduring the course of the concentration. The "operation is continued until the solution tests about 60 B. (hot) after the removal of the undissolved material, which is largely if not wholly sodium sulfate.

(b) The process for making mono-sodium phosphate from disodium phosphate and sulfuric acid may be modified in the following way: Treat di-sodium phosphate .with sulfuric acid as described above, but

. instead of concentrating the mixture by boiling, add just suflicient water to effect complete solution of any solid salt in the mixture at boiling temperature. The solution should then test about 40 B., at boiling temperature. Allow the solution to cool and crystallize. Separate the crystals which are sodium sulfate containing a relatively small proportion of mono sodium phosphate. These are returned to the sodium phosphate process described in Patent No. 744,128. The mother liquor is concentrated to approximately 50 and allowed to cool and crystallize. The crystal product is mono-sodium phosphate. The mother liquor is again concentrated to 50 B. and cooled and crystallized. The crystal product is The product is mono-so-' mono-sodium phosphate. This 'concentrating and cooling is continued until the monosodium phosphate obtained runs too high in sulfate for commercial purposes, when the material still remaining is returned to the sodium phosphate process described in Petent No. 744.128.

B. Using hydrochl$ acid as the added Example II.

0. Using nitric acid as the added acid.

Emample III.

Neutralize crystallized di-sodium phosphate with nitric acid, using methyl orange as indicator. Concentrate by evaporation to 48 B. (test not filtered), allow to cool. Separate the undissolved material which is principally sodium nitrate, by filtering or other known method. Concentrate the filtrate to 50 B., cool and crystallize. The crystals are mono-sodium phosphate. The

mother liquor may be concentrated and crystallized. The final liquors including the sodium nitratecrystals separated above, are used for making sodium phosphate.

D. Using acetic acid as the added acid. Example IV.

To 100 parts of anhydrous di-sodium phosphate, add. 210 parts of glacial acetic acid containing 99% of acetic acid, C,H O digest the mixture for one hour at 212 F.; filter hot; the residue on the filter is crude mono-sodium phosphate and the filtrate is sodium acetate and acetic acid and contains practically no mono-sodium phosphate.

The several grades of mono-sodium phosphate obtained in all the foregoing examples are, if necessary, further purified by suitable crystallization; in the several examples given 'here there is indicated the probably most advantageous conditions of strength and temperature of solutions for achieving further purification; applyingthe ordinary experience and rules obtaining in such practice, the mono-sodium phosphate can be freed from accompanying salts of the added 'acids to any extent needful in commercial 13,)

filter boiling hot; the residue on the filter'is operation. In the preceding examples, furthermore, tri-sodium phosphate may be used instead of di-sodium phosphate with correspondingly similar results.

-. ornnAcrrrzo WITH DI-POTASSIUM PHOSPHATE. E. Using sulfuric acid as the added acid. Ewample V.

(a) Neutralize a solution of di-potassium phosphate dissolved in water, which solution has a specific gravity of about 1.28 with 98%. sulfuric acid using methyl orange as indicator; concentrate by the aid of heat until the supernatantliquor shows 42 B.;

practically potassium sulfate. Cool the filtrate, stir while crystallizing and filter; the residue on the filter is a fair grade of crude -mono-potassium phosphate; concentrate the filtrate by the aid of heat until it shows 42 B.; cool; stir while'crystallizing; filter; the residue on the filter 'is likewise a fair grade of crude mono-potassium phosphate; the filtrate and the residue above containing principally potassium sulfate; may be returned to the potassium phosphate process.

(b) Instead of stopping the concentration 'of the neutralized mono-potassium phosphate of the preceding at 42 B. -it may also be found advantageous to continue the "concentration to 46 B. filter hot; the residue on the filter is principally potassium,

sulfate; bring the filtrate to a boil; add

enough hot water to make it test 36 B.

when hot; cool; stir while crystallizing; filter; the residue on thefilter is a fair grade of mono-potassium phosphate; this filtrate and the residueabove containing principally potassiumsulfate, may be returned to the potassium phosphate process.

e F. Using hydrochloric acid as the added acid.

Ewample VI.

(a) Separating crude mono potassium phos hate from the hot liquor, leaving most 10% t e potassium chZorid in the liquor:-

eutrahze a solution of di-potassium phosphate in water which solution has a specific gravity of about 1.28 with hydrochloric acld (sp. gr. 1.19) using methyl orange as indicator; boil the mixture untila solid begins to separate; continue the boiling until the appearance of the separated soli begins to change; filter boiling hot; the residue on the filter is a fair grade of crude mono-potas- I sium phos hate. The filtrate which tests approximate y 38 B. may be treated as are the final filtrates in the examples under mono-sodium phosphate.

(b) Separating the crude monopotassium phosphate from themcst of the potas-' sium chtorid by crg staZZization.Proceed as under Example VI (a), but stop the bpiling acid (sp.

just when solid matter first begins to separate out; now cool, stir while crystallizing and filter; the residue on the filter-is inthe main mono-potassium phosphate; the

filtrate may be treated as is the final filtrate in Example VI (a).

, 0 Using nitric acid as the added acid.

Example VII =Neutralize a solution of di-potassium phosphate in water, which solution has a specific gravity of about 1.28 with nitric gr. 1.42) boil down until solid matter begins to separate; continue the boiling until the supernatant liquor after testing 44 B. has risen to 445 B.; filter hot; the

residue on the filter is principally monopotassium phosphate. This filtrate may be treated like the final filtrate in Example VI (a). y

H. Using acetic acid as theadded acid.

' Example VIII.

(a) Separating the mono-potassium phos phate by crystallizing it from the potassium acetate.-To a solution of di-potassium phosphate in water which solution has a specific gravity of about 1.28, add glacial phate from the hot Ziguor tearing most of e the potassiwm acetate in the hot liquor.

' Proceed as underExample VIII (a) but boil the solution obtained after treatment with acetic acid as theredescribed until it tests 27.5 B.; filter'hot; the residue on the filter is a good grade of mono-potassium phosphate; the filtrate may be treated like the final filtrates under Example VI (a).

I claim: 1 1. The process of making mono-alkali an alkali metal phosphate with an acid free from phosphorus and separatingthe mono -metal phosphate which consists in treating alkali metal phosphate and the salt of the;

added acid produced, in the non-alcoholic 1i uid, substantially as and for the purpose escribed.

an alkali metal phosphate with an acid fre from phosphorus and sefpa'rating the mono alkali metal phosphate r cm the salt of the presence of a 12 s 2. The process ofmaking mono-alkali metal phosphate which consists in treating' added acid reduced, by concentrating the solution of t e mixture to such a point where phosphate which consists intreating sodium phosphate with an acid free from phos- -phorus and separating the mono-sodium metal phosphate from an a alimetal salt f phosphate from the salt of the added acid produced, by concentrating the solution of the mixture to-such a'point where substan-' tially all of the sodium salt of the added acid separates out in solid form and separatin the'solid from the liquid portion.

4. he process of making mono-sodium phosphate which consists in treating sodium phosphate with sulfuric acid and sepa-' rating the mono-sodium hosphate from the sodium sulfate produce by concentrating the solution of the mixture to such a point where substantially all of the sodium sulfate separates out in solid form and separating the solid from the liquid portion.

5 Process of separatin monoalkali of an acid free from phosphorus which comprises concentrating the solution of the mixtureto such a point Where substantially all of one of these salts separates out in solid form and separating the solid from the liquid portion.

6. Process 1 of separating mono-sodium phosphate fromthe sodium salt of an acid free from phosphorus which comprises concentrating the solution of the mixture to such a point where substantially, all of the sodium salt of the added acid separates out in solid form and separating the solid from the liguid portion.

rocess of separating mono-sodium phosphate from sodium sulfate which comprises concentrating the solution of the mixture to such a point where substantially all of the sodium sulfate separatesout in solid form and separating the solid from the liquid ortion. v l

8. e cyclic process of making monoalkali metal phosphate which consists in treating an alkali metal phosphate with an acid free from phosphorus, separating the mono-alkali metal phosphate and the salt of the acid produced, converting the sepations,.substantially as and for the purpose 7 described.

9. The cyclic process of making-monoalkali metal phosphate which consists in first -making alkali metal phosphate by treating a phosphate containing substance with an acid alkali metal sulfate and furnacing the result in the presence of carbonaceous material, then treating the alkali metal phosphate, thus produced, with an acid free from phosphorus to produce monoalkali metal phosphate and an alkali metal salt of the added acid, then separating the last-mentioned salts, then converting the separated alkali salt of the added acid into acid alkali sulfate and finally utilizing the last mentioned acid alkali sulfatein a repetition of the above operations, substantially as and for the purpose described.

10. The cyclic process of making monoalkali metal phosphate which consists in first making tri-alkali metal phosphate by treating a phosphate containing substance with an acid alkali metal sulfate andfurnacing the result in the presence of carbonaceous material, then treating the tri-alkali metal phosphate, thus produced, with sulfuric acid to produce mono-alkali metal phosphate and an alkalimetal sulfate, then separating the last mentioned salts, then conve'rting t e separated alkali metal sulfate into acid alkali metal sulfate and finally utilizing the last mentioned acid alkali metal sulfate. in a repetition of the above operations, substantially as and for the purposedescribed.

- Witnesses:

Home: W. HILLYER, BERNHARD Hnssn.

EMERSON H. STRICKLER. 

